great I also think that the main character should have powers like x-ray,mind reading ect.
Can't play(Android only) but a good way to spice things up is to add a shady character/other demoness that will give you other abilities like x-ray and trance(let's you grope and eventually undress girls without reaction) in return for favors and information about your contractor that could lead to you gaining some control of your contract(either saving your soul or supercharging your existing abilities)
why not give the player the ability to effect certain individuals in order to change their assets, like say giving them the power to make a girl's rear end larger or even make them taller in general, most games i see only have growth or shrinking happen due to corruption in general, so having the ability to control when it happens would be a new detail that would help it stand out from the rest